1. Field of the Invention
The present invention relates generally to methods and systems for mapping the geographic position and path of conduits and pipelines. The present invention relates more specifically to an apparatus and an associated method for internally following, tracking, and recording the position and path of a pipeline or conduit with a free-moving motion and orientation sensor.
2. Description of the Related Art
Underground pipelines make up a vast network of conduits carrying a wide range of materials within and between all countries of the world through all types of terrain. While some such pipelines and conduits are exposed to view, most are buried in the ground or under other manmade structures such that they are occluded from view. Economies rely heavily on the proper functioning of these pipelines, especially as they supply energy materials, such as oil and gas, to locations remote from the production of the materials. In many instances, as a pipeline corrodes, it becomes necessary to repair or replace segments of the pipeline. In most cases, when this occurs, the pipeline must be uncovered to identify and locate that portion of the pipeline that requires repair. A major obstacle to this task, for the majority of pipelines that are occluded from view, is knowing where to dig or otherwise uncover the pipeline, as the location of the pipeline is often unknown or inaccurately recorded. It therefore becomes desirable, if not essential, to map the pipeline's location for the most accurate and efficient effort at locating and exposing the pipe for later repair.
Various systems have been developed for the inspection of pipelines using sensors designed to travel inside the pipe and to carry out a variety of measurements on the characteristics of the pipe walls and the overall integrity of the conduit system. Some of these sensor systems are designed to move “freely” within a pipe such as on wheeled carts and the like, sized and structured to travel along the length of the pipe, within the typically circular cross-section with or without the fluid or gas inside the pipe. A group of such systems are referred to generically as “pigs” or pipeline inspection gauges.
Inertial sensors have been placed on pigs (pipelines inspection gauges) in the past, primarily to track and determine changing elevations in a pipeline path. Examples of such systems are disclosed in a number of issued U.S. patents including the following:
U.S. Pat. No. 6,243,657 issued to Tuck et al. entitled Method and Apparatus for Determining Location of Characteristics of a Pipeline, describes a pipeline inspection and defect mapping system utilizing a pig with an inertial measurement component and a pipeline inspection component for defect detection. The system also utilizes several magnetic logging devices positioned at precisely known locations along the pipeline for interaction with the pig as it passes through the pipe. Post processing incorporates data from the logging devices and the pig based sensor, primarily to derive the location of the detected defects.
U.S. Pat. Nos. 6,553,322 and 6,768,959, each issued to Ignagni and each entitled Apparatus and Method for Accurate Pipeline Surveying, describe a pipeline surveying system that includes a pipeline pig operable in conjunction with a previously determined global positioning system survey. The pig utilizes an inertial measurement unit and correlates the measured profile with the GPS survey.
These previously utilized approaches, however, are limited, in that the pigs are typically wheeled carts, and therefore have limits as to where and how they may propagate through the pipeline. Sharp angled turns, valve structures, and other such internal “obstructions” often prevent the easy movement of a wheeled or track based pig within the pipe. Such systems therefore often only yield a vertical profile of a pipe, typically over a long generally straight distance.
Other efforts in the industry have focused on miniaturized sensor systems capable of movement in conjunction with the gas or fluid flow through a conduit, pipeline, or borehole environment. Examples of these systems include those described in U.S. Pat. No. 6,324,904 issued to Ishikawa et al. entitled Miniature Pump Through Sensor Modules; U.S. Pat. No. 6,935,425 issued to Aronstam entitled Method for Utilizing Microflowable Devices for Pipeline Inspections; U.S. Pat. No. 6,745,833 issued to Aronstam et al. entitled Method of Utilizing Flowable Devices in Wellbores; and U.S. Pat. No. 6,814,179 issued to Corrigan et al. entitled Seismic Sensing Apparatus and Method with High-G Shock Isolation.
In addition, a number of efforts have been made in the past to configure sensors that may be allowed to freely move through pipeline systems and carry out some type of inspection or monitoring of the pipeline walls or contents. Examples of such efforts include U.S. Pat. No. 5,485,148 issued to Tseng entitled Pipeline Fluid Travel Monitoring System; U.S. Pat. No. 5,126,980 issued to Sallas et al. entitled Self-Orienting Vertically Sensitive Accelerometer; U.S. Pat. No. 3,212,340 issued to Benckert entitled Inertial Double Integrating Accelerometer; U.S. Pat. No. 6,453,745 issued to Jalkanen entitled Sensor Device for the Three-Dimensional Measurement of an Attitude or Acceleration; and U.S. Pat. No. 6,261,247 issued to Ishikawa et al. entitled Position Sensing System.
Some efforts in the past to generally measure the motion of an object with inertial references have utilized sensors with a “sphere-in-sphere” construction. Examples of some of these systems include those described in U.S. Pat. No. 3,056,303 issued to Naylor entitled Hydraulically and Spherically Supported Inertial Reference (the external sphere is fixed to a vehicle frame); U.S. Pat. No. 4,345,473 issued to Bernie entitled Vertical Component Accelerometer; U.S. Pat. No. 5,046,056 issued to Sallas et al. entitled Self-Orienting Vertically Sensitive Accelerometer; and U.S. Pat. No. 6,679,118 issued to Esashi et al. entitled Accelerometer and Spherical Sensor Type Measuring Instrument. The detailed disclosures of each of these prior U.S. patents are incorporated herein by reference.
All of the efforts in the past have generally failed to provide a fully self contained sensor system capable of free motion within a pipeline, that can create a record of orientation and motion sufficient to produce positional information (with respect to time) from which a map of the pipeline might be generated. The systems previously utilized either combine the movable sensor with fixed sensors or reference triggers along the path of the pipe (which of course requires some clear knowledge of the location of the pipeline) or involve sensors that must travel on frames that are incapable of easily traversing the internal obstructions typically associated with oil and gas pipelines or the like.
It would be desirable to have a freely moving sensor of the sphere-in-sphere configuration where both spherical structures were free to move within the confines of a pipeline, and where the orientation and position of at least one part of the sensor could be constantly tracked. It would be desirable if one part of the sensor could readily “absorb” the tumbling motion experienced by the sensor system as a whole and allow a remaining part of the sensor system to maintain a stable (measurable) orientation such that sensor components might track changes in the orientation and position of the sensor system as a whole.